arXiv subjects

Xiejin Li

Publications and source records attributed to Xiejin Li.

6 recordsLinked to original sources

arXiv2026

Environmental dependence of Type Ia supernova standardization on the local luminosity-weighted age

Context. The dependence of Type Ia supernova (SN Ia) standardised luminosity on host galaxy properties is a major source of uncertainty in cosmology. As next-generation surveys like LSST and HLTDS reduce statistical uncertainties, cosmological precision will be limited by astrophysical systematics. However, the empirical mass step, an indirect global proxy, may obscure the physical link to the progenitor environment. Aims. We test whether local luminosity-weighted age (LWA), used as a statistical proxy for the age of the stellar population associated with SN Ia progenitors, is more closely related to the physical driver of standardised-luminosity variations than host galaxy mass. Methods. Using SDSS-MaNGA Pipe3D, we extracted local LWA within a 1 kpc aperture for 56 SNe Ia and performed a joint likelihood analysis of local age and mass effects on Hubble residuals. Results. SNe Ia in younger environments are significantly fainter than those in older ones, with a step amplitude of 0.163 mag (5.2 sigma) after standardisation. Global and local mass steps are initially observed (0.071 mag, 2.0 sigma and 0.087 mag, 2.4 sigma), but both become insignificant when age and mass are fitted simultaneously: the global mass step decreases to 0.028 mag (0.9 sigma), while the age step remains robust at 0.156 mag (4.9 sigma). Similarly, the local mass step becomes insignificant (0.012 mag, 0.3 sigma), whereas the age step persists at 0.157 mag (4.4 sigma). The weighted Hubble residual decreases from 0.1550 to 0.1376 mag after introducing the local LWA step. Conclusions. The mass step is substantially reduced when local LWA is included. The inferred dark energy equation of state parameter (w) could be affected by local LWA, highlighting the importance of environmental effects for next-generation SN Ia cosmology.

astro-ph.CO↗

arXiv2026

When Galaxies Refuel: Evolution of the Perturbed Spiral Galaxy NGC1385

The spiral galaxy NGC 1385 is characterized by a vigorous and protracted history of star formation, particularly in its central regions, leading to a current star formation rate that surpasses those of comparable systems. We analyze the evolution history of the galaxy using spatially resolved optical and submillimeter spectroscopy obtained from the PHANGS survey combined with WALLABY radio survey data. We construct radial distributions of star formation rate and the interstellar medium (ISM) neutral and molecular gas mass surface densities and measure the metallicity distribution of the stellar populations using a refined full-spectral fitting population synthesis method together with a determination of ISM oxygen abundances using H\,II region emission lines. The metallicities of the young stars and the ISM are similar and show an almost flat distribution. This is crucially different from previous work which had found a positive gradient for the average metallicities of the stars. We fit a chemical evolution model (incorporating gas infall, outflow, and radial inflow) to the observed data of NGC\,1385. Based on this fit, the evolution of NGC\,1385 is characterized by the typical inside-out disk formation of spiral galaxies -- even though our model does not assume an a priori shorter gas infall timescale for the inner disk than for the outer disk. However, the galaxy has experienced sustained star formation over gigayear timescales with a star formation efficiency a factor of two higher than normal. This explains the high metallicity of the young stars of 0.15 to 0.2\,dex higher than solar and the flat distribution of metallicity across the disk. The model predictions for the metallicities of the stars align well with the observed values, supporting the robustness of both our refined spectral fitting analysis and the inferred evolutionary scenario.

astro-ph.GA↗

arXiv2026

Radial Profiles of Binary Fraction in Elliptical Galaxies

The radial profile of binary fraction may vary with environment and is of significant importance for studying the formation mechanisms of binary stars and their dynamical evolution within globular clusters (GCs) and galaxies. However, existing studies remain limited to the Milky Way and its neighboring galaxies. Leveraging the method proposed by Zhang et al. for estimating the variation of binary fraction from integrated spectral features, we analyze a sample of 513 elliptical galaxies drawn from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey to measure their radial binary fraction profiles. Our results show that after accounting for the effect induced by radial variations in the stellar population (SP), the median SP-subtracted binary fraction, $r_{\rm b,sub}^{\rm med}$, becomes approximately flat. For nearly all elliptical galaxies in our sample, the variation in binary fraction relative to the galaxy center at $1R_e$ is less than 5%. No clear correlation is found between the binary fraction gradient and the gradients of SP properties. Moreover, we also compare differences between ultraviolet (UV) upturn and non-UV upturn galaxies. The overall binary fraction profiles and SP properties of the non-UV upturn galaxies in our sample are comparable to those of the UV upturn galaxies. This similarity may arise from the presence of residual star formation (RSF) in the non-UV upturn systems.

astro-ph.GA↗

arXiv2026

BayeSED-GALAXIES II. Bayesian full spectrum analysis of galaxies and application in the CSST wide-field slitless spectroscopy survey

The China Space Station Telescope (CSST) will conduct wide-field multiband photometric imaging and slitless spectroscopic surveys, advancing cosmology and galaxy evolution studies. Achieving CSST's cosmological goals requires precise redshifts ($σ_{\rm NMAD}\lesssim 0.002-0.005$) from low-resolution ($R\sim200$) and potentially blended slitless spectra. We present BayeSED3, extended for Bayesian full-spectrum analysis, including nebular emission modeling (via \textsc{Cloudy}) and a Bayesian treatment of the model scaling factor, improving reliability over optimization methods for low SNR spectra. Validated on realistic mock data generated with the CESS emulator (median SNR=1.65, including instrumental and self-blending effects), our method achieves excellent redshift precision with three-band (GU+GV+GI) spectroscopy: $σ_{\rm NMAD}=0.0008$ ($\sim$80% success) for star-forming and $σ_{\rm NMAD}=0.0015$ ($\sim$50% success) for quiescent galaxies. Stellar mass ($σ_{\rm NMAD}\approx0.015$ dex for SF, $\approx0.016$ dex for quiescent) and SFR ($σ_{\rm NMAD}\approx0.05$ dex for SF, especially at SNR>1) are reliably recovered. Self-blending increases scatter by $\gtrsim30%$, but combining spectroscopy with CSST's seven-band photometry significantly improves accuracy, especially for quiescent galaxies and data-limited cases. Single-band spectroscopy plus photometry yields reasonable redshifts: GU+photometry is limited, GI+photometry gives >60% (SF) and >40% (quiescent) success at $σ_{\rm NMAD}\lesssim0.002$, GV+photometry gives >35% (SF) and $\sim$40% (quiescent) at similar precision. The Bayesian framework offers a powerful method for accurate galaxy characterization, enhancing CSST's scientific outcomes despite the challenges of slitless spectroscopy.

astro-ph.GA↗

arXiv2025

A Morphological Study on AGN-host Dwarf Galaxies

The study of morphology in galaxies offers a convenient and quantitative method to measure the shapes and characteristics of galaxy light distribution that reflect the evolutionary history. For AGN-host dwarf galaxies, however, there is a lack of detailed studies on their morphologies. In this work, we compile a relatively large sample ($\sim$400 members) of local AGN-host dwarf ($M_{\star}\leq10^{9.5} M_{\odot}$ and $z<0.055$) galaxies selected via various methods. We use the $grz$ bands images from DESI DR10 and the Python package statmorph to measure non-parametric coefficients. We also carry out visual inspection with the assistance of deep learning to classify these galaxies into early-type (ETGs), late-type (LTGs) galaxies, and mergers, and find that about 37%, 44%, and 13% of the total sample sources are ETGs, LTGs, and mergers, respectively. In comparison to normal dwarf galaxies, AGN-host dwarfs have a higher probability to be LTGs, and a lower merger rate, indicating that mergers/interactions are not the primary driver of AGN activities. Among the subsamples selected with different methods, the BPT sample has the highest fraction of ETGs, the variability sample consists of the largest fraction of LTGs, and the mid-IR sample contains the most mergers.

astro-ph.GA↗

arXiv2024

Stellar Populations of AGN-host Dwarf Galaxies Selected with Different Methods

In this paper we investigate the stellar populations and star formation histories of 235 active galactic nuclei (AGN)-host dwarf galaxies, consisting of four samples identified separately with different methods (i.e., radio, X-ray, mid-IR and variability), utilizing the synthesis code STARLIGHT and spectra from the Sloan Digital Sky Survey (SDSS) Data Release 8. Our results show that the variability sample is the oldest, while the mid-IR sample is the youngest, for which the luminosity at 4020 Å is dominated ($>50\%$) by the young population ($t<10^8$ yr). The light-weighted mean stellar age of the whole sample is in general about 0.7 dex younger than the optical sample studied in Cai et al. We compare the population results between fitting models with and without a power-law (PL) component and find that the neglect of a PL component would lead to an under- and over-estimation by 0.2 and 0.1 dex for the light- and mass-weighted mean stellar age, respectively, for our sample of dwarf galaxies, which has a mean fractional contribution of $\sim$16\% from the AGN. In addition, we obtain further evidence for a possible suppression of star formation in the host galaxy by the central AGN. We also find that there exists an anti-correlation between the extinction-corrected [O\,{\sc iii}] luminosity and light-weighted mean stellar age, confirming our previous finding that there is a physical connection between AGN and star-forming activities in AGN-host dwarfs.

astro-ph.GA↗